The present invention relates to a method for placing and re-melting a multitude of shaped parts of solder material on a bond pad arrangement of a substrate, said bond pad arrangement comprising a multitude of bond pads, and for subsequent re-melting of the shaped parts of solder material on the bond pads. Furthermore, the present invention relates to a device suitable for implementing this method.
Methods of the type mentioned above are used for example in so-called wafer bumping, in the production of so-called chip-size packages, or in the production of ball grid arrays. Basically, the above-mentioned methods involve the production of a multitude of uniformly shaped bond pad metallisation areas or contact metallisation areas in a specified arrangement, on a substrate surface. To this effect, the following methods have been used up to now. In the first method, placement or arrangement of solder material deposits on the bond pads takes place as part of an individual placement method, and subsequent re-melting takes place by a separate application of heat energy, for example laser energy, to the solder material deposits or to shaped parts of solder material. In the second method, for example in a mask application process, solder material deposits are applied as a paste-like material, and subsequent remelting is carried out in an oven, at the same time for all the solder material deposits.
The first method is particularly advantageous in that as a result of individual application of thermal energy to the solder material deposits or to the shaped parts of solder material, in particular in the case where laser energy is used, the substrate is exposed to as little thermal load as possible. However, this method is also correspondingly slow in its implementation. The second method, in particular due to the rapidly progressing re-melting process, makes it possible to achieve a large throughput with accordingly large numbers being produced. However, the implementation of such a method is associated with considerable production costs, in particular due to the considerable expense of the equipment required. Furthermore, depending on the type of the substrate to be treated in this way, problems will be encountered due to the substantial thermal loads experienced.
It is thus the object of the present invention to propose a method of the type mentioned in the introduction, and to propose a device which is suitable for implementing such a method, which device and method make it possible to place and subsequently re-melt a multitude of shaped parts of solder material on bond pads of a substrate as economically as possible while at the same time keeping thermal exposure of the substrate as low as possible.
This object is achieved by a method with the characteristics of claim 1, and by a device with the characteristics of claim 10 or 15.
In the method according to the invention, first a template device which comprises a multitude of template apertures for accommodating shaped parts of solder materials, is arranged opposite a substrate comprising a bond pad arrangement such that the shaped parts of solder material are associated with the individual bond pads. Then follows application of laser energy, from a laser device which is arranged at the rear of the template device, to the shaped parts of solder material accommodated in the template apertures, such that laser energy is applied through the template device, to the shaped parts of solder material.
Thus the process according to the invention combines a template method which is suitable for carrying out a particularly time-saving placement action, with said method, from the point of view of thermal load, involving a laser re-melting process which is particularly gentle on the substrate.
In a particularly preferred variant of the method, singling-out, which is necessary for applying the individual shaped parts of solder material, takes place in the template device itself, from a quantity of shaped parts of solder material accommodated in the template device, by filling of the template apertures which are arranged in an aperture screen of the template device. In this variant of the method, the template device itself serves as a reservoir for the shaped parts of solder material, thus obviating the need for a separate feed device for feeding shaped parts of solder material to the template device.
In a variant of the method which is also very advantageous, singling out of the shaped parts of solder material by the template device takes place by removing shaped parts of solder material from a quantity of shaped parts of solder material arranged outside the template device, such that during removal, the template device""s template apertures, which are arranged in an aperture screen, are filled.
In this variant, the template device itself serves as a removal device, so that there is no need to provide a separate device for supplying shaped parts of solder material to the template device and for removing shaped parts of solder material from said template device.
Irrespective of the choice of the above-mentioned variants, it is advantageous if prior to the application of laser energy to the shaped parts of solder material, scanning of the template apertures using an optical scanning device for detecting shaped parts of solder material, takes place.
This makes it possible to detect any defective spots very early, i.e. prior to any quality assurance test which may take place after the re-melting action. Furthermore, the laser device can be made to be triggered only if a shaped part of solder material is present at the particular bond pad, thus preventing any thermal damage to the substrate due to the bond pad being directly exposed to laser energy.
It has also been shown to be particularly advantageous if application of laser energy to the shaped parts of solder material takes place via the optical scanning device which is already being used for detecting shaped parts of solder material.
If that variant of the method is used where, as explained above, the template device itself serves as a reservoir for the shaped parts of solder material, it is advantageous if filling of the template apertures arranged in an aperture screen of the template device, takes place by means of a filling chamber which can be moved over the aperture screen and which is open towards said aperture screen.
A further advantageous option when realising the variant of the method according to the invention where the template device itself serves as a reservoir for the shaped parts of solder material, consists of filling the template apertures which are arranged in an aperture screen of the template device by means of a paddle-wheel device which can be moved parallel to the surface of the aperture screen, rotating on its movement axis.
When realising the variant described above, of the method according to the invention, where the template device itself serves as a removal device for removing the shaped parts of solder material from a reservoir for shaped parts of solder material, it is advantageous if filling of the template apertures arranged in the aperture screen of the template device, takes place by means of pressure below atmospheric.
Irrespective of the variants, described above, for implementing the process according to the invention, in any case the shaped parts of solder material accommodated in the template apertures can be exposed to pressure so as to generate contact with the bond pads, by means of pressure above atmospheric applied in the template device. It is also possible to generate contact via mechanical pressure of the template device itself.
The device according to the invention, which is particularly suitable for implementing the method according to the invention, provides for a template device comprising a container for accommodating a quantity of shaped parts of solder material, with the container comprising a container wall arrangement, designed as an aperture screen, for conveying shaped parts of solder material to the bond pad arrangement, and with the aperture screen comprising a singling-out device such that shaped parts of solder material which have been singled out from the quantity of shaped parts of solder material and allocated to individual bond pads of the bond pad arrangement, are arranged so as to be exposed, in template apertures of the aperture screen, and thus can be exposed to laser energy by means of a laser device arranged at the rear of the template device.
According to a preferred embodiment, the singling-out device is designed so that it can be moved over the aperture screen. The singling-out device can be a filling chamber which can be moved over the aperture screen, said filling chamber being open towards the aperture screen.
A further advantageous option consists of the singling-out device being designed as a paddle-wheel device which can be moved over the aperture screen, with radially open transport compartments delimited by paddles of a paddle wheel of the paddle-wheel device.
If irrespective of its design, the singling-out device is accommodated in a closed space which is formed by the template device whose rear wall, which is arranged opposite the aperture screen, is made so as to be transparent, it is possible to overlay application of the individual shaped parts of solder material to the bond pads of the bond pad arrangement of the substrate, with pressure above atmospheric. The same also applies to the re-melting process. It is particularly advantageous in this context if a protective gas atmosphere is used to generate the pressure above atmospheric.
In an alternative embodiment of the device according to the invention, the template device itself is a singling-out device, comprising a housing with an aperture screen, said aperture screen comprising a multitude of template apertures for accommodating shaped parts of solder material, and comprising a transparent rear wall, arranged opposite the aperture screen.
If pressure below atmospheric is applied to such a template device, it can itself serve as a singling-out device and/or removal device for removing shaped parts of solder materials from a reservoir containing shaped parts of solder material. In this case, due to removal of the shaped parts of solder material from the reservoir, automatic filling of the template apertures takes place as a result of the application of pressure below atmospheric.
If the diameter of the template apertures formed in the aperture screen is smaller than the smallest diameter of the shaped parts of solder material, it is possible, when pressure below atmospheric is applied, to hold the shaped parts of solder material by partial vacuum to the aperture cross-section of the template apertures so that at the same time as singling-out, exposed arrangement of the shaped parts of solder material results which makes it possible, via the template device, to mechanically press the shaped parts of solder material against the bond pads of the bond pad arrangement.
If the diameter of the template apertures formed in the aperture screen is larger than the largest diameter of the shaped parts of solder material, and if the distance between the aperture screen and the rear wall is smaller than the smallest diameter of the shaped parts of solder material, it is possible to arrange the shaped parts of solder material in the interior of the template device, while maintaining the singled-out arrangement, so as to be able to carry out the subsequent re-melting action to a very large extent within the template device.
It is particularly advantageous if the wall structure of the aperture screen and/or of the sidewalls of the filling chamber, which can be moved over the aperture screen, is flexible across the area of the aperture screen. This makes it possible to achieve an aperture screen which contacts the substrate surface to a very large extent even if said substrate surface is uneven.
To this effect, the wall structure can comprise at least three layers, with a flexible compression layer sandwiched between two wear-resistant surface layers. It is particularly advantageous if the compression layer is made from a plastic material, and the surface layers are made from metal.